Durable Copper and Iron SCR Catalysts for Mobile Diesel and Dual-Fuel Applications

The latest emission regulations for mobile and stationary applications require the use of aftertreatment methods for NO_x and diesel particulate filters (DPF) for particulate matter (PM). SCR catalysts were evaluated by laboratory experiments and the most promising SCR catalysts were also scaled up to full-size. Development with copper (Cu) and iron (Fe) on zeolitic materials (Beta, ZSM-5, SAPO, chabazite) has resulted in the new generation of thermally durable SCR (selective catalytic reduction) catalysts, which have also an improved sulfur tolerance and a low N₂O formation tendency. Opposite to Cu on Beta and ZSM-5, Cu on chabazite and SAPO showed clearly lower N₂O formation. Cu-SCR catalysts had a low dependency on NO₂/NO_x but Fe-SCR catalysts required a higher NO₂/NO_x ratio (>0.3) to keep a high NO_x efficiency. The decomposition of sulfates on the durable Cu- and Fe-SCR catalysts was investigated by temperature programmed oxidation (TPO) and reduction (TPR) methods to find the appropriate conditions for desulfation.

Full-scale SCR systems with diesel oxidation catalysts (DOC) were evaluated by engine bench experiments. The Cu-SCR based catalysts showed a wide operation window, resulting in NO_x conversions above 95% as fresh and thermally aged at 650-750°C. The platinum containing ammonia slip catalyst (ASC) is usually integrated as a short zone on the SCR unit and its main role is to prevent slip in transient conditions.